And, of course, the disagreeing reader doesn't need to be in your head: if, as you're starting work on an essay, you ask a few people around you what they think of topic X (or of your idea about X) and keep alert for uncongenial remarks in class discussion and in assigned readings, you'll encounter a useful disagreement somewhere. Awareness of this disagreement, however you use it in your essay, will force you to sharpen your own thinking as you compose. If you come to find the counterargument truer than your thesis, consider making it your thesis and turning your original thesis into a counterargument. If you manage to draft an essay without imagining a counterargument, make yourself imagine one before you revise and see if you can integrate it.
The NSA intercepts telephone and Internet communications of over a billion people worldwide, seeking information on foreign politics, military developments, terrorist activity, pertinet economic developments,  and "commercial secrets".  A dedicated unit of the NSA locates targets for the CIA for extrajudicial assassination in the Middle East.  The NSA has also spied extensively on the European Union, the United Nations and numerous governments including allies and trading partners in Europe, South America and Asia.